This invention pertains to a particular joint between a turbine ring, which has the function of edging the turbine by delimiting the gas flow stream, and a part called spacer which belongs to the structure of the turbine.
A modern joint is described in U.S. Pat. No. 5,197,853 and illustrated in FIG. 4. A turbine body 1 bears a spacer 2 which itself bears a ring 3. The jointing parts of the ring 3 with the spacer 2 comprise, upstream, a spacer hook 4 and a ring hook 5 which are fitted into one another: mounting of the ring 3 is performed by pushing the end of the ring hook 5 into the recess of the spacer hook 4, then pivoting the ring 3 so as to approach its opposite end, located downstream, to that of the spacer 2; the other jointing parts 6 are located on these downstream ends.
It concerns a spacer rim 7 first directed radially inwards, then downstream, and a ring rim 8, directed radially outwards then axially downstream; the ring rim 8 is formed as a circular groove forming a mortise 9 opening radially outwards in which is accommodated a portion of the spacer rim 7, which thus plays the role of a tenon, formed as a rib extending radially inwards. The end of the tenon has two parallel flanges 10 and 11 and they come and abut against the bottom of the mortise 9. Clips 12 are then fixed over the parallel ends of rims 7 and 8, so that its legs 13 and 14 clasp them and prevent them from coming apart. Separation between spacer 2 and ring 3 is also prevented by the fitting together of hooks 4 and 5 on the other side; the ring 3 may slightly play in the axial direction on spacer 2 within an excursion, the length of which is defined by the total play between the flanks of the flanges 10 and 11 and the flanks of the mortise 9, at the locations marked by reference numbers 15 and 16. These slipping movements are generated by thermal expansions and by downstream aerodynamic forces, which are produced by the gases of the central stream of the turbine.
Thus, the sealing between a chamber 17 surrounded by the spacer 3 and the outside is established downstream by the contact of cylindrical surfaces formed at the end of the flanges 10 and 11 and at the bottom of the mortise 9, and an axial play in the motion of ring 3 in spacer 2 remains around the spacer rim 7, between the flanks of the mortise 9. The axial play creates an air leak downstream from the system, but however it must remain in order to maintain the mounting of the ring by a swinging movement.
U.S. Pat. No. 5,669,757 relates to an enhancement of this layout, wherein the mortise is located on the spacer rim and its downstream flank is borne by a removable annular angle, and the tenon is located on the ring rim: mounting of the ring may then be performed by a purely axial movement and the distance between the upstream end of the ring and an adjacent ring may be reduced as no swinging movement can produce a blocking at this location. The angle is then inserted with a radial movement into a groove of the spacer support in order to close the mortise and the fastening clips are finally introduced under the rims and the angle in order to maintain the latter in place.
This enhancement has no reinforcing effect on the seal downstream as an axial play of the tenon in the mortise remains, either by design or as a consequence of deformations undergone by the relatively flexible angle and easy to swing when the angle pushes it downstream. The clips have then the extra function of opposing movements of the angle, which they are unable to do completely but this requires that they be given a circular extension of a complete turn. The actual presence of the angle which is an extra part, reduces the mechanical strength of the joint and makes it manufacturing complicated.
The invention relates to an enhanced joint between a turbine ring and its spacer, wherein the basics of this prior joint are substantially reinstated (fixation in the radial direction by hooks fitted together on one side, and by abutment faces of concentric rims on the other side; and limitation of the axial movement by a mortise and tenon system on this other side), but is superior as regards the cohesion of the fit, the protection of the spacer against excessive heatings and the mechanical strength.
It comprises various enhancements, the most notable of which is perhaps that the tenon and the mortise are located upstream from the abutment rims, which means that the seal and axial retention are provided by different portions separated from the spacer and the ring.
The advantage that the tenon and mortise give into the interior chamber (17 in FIG. 4), which is generally ventilated by fresh gas, is now obtained and thus are less exposed to heatings and to expansions. The slippings imposed on the seal surfaces of the rims are then reduced. They may even be virtually suppressed if the tenon and mortise are jointed with zero axial play, which may be obtained if the mortise is limited on one side by a flexible tab which deforms upon inserting the tenon therein. The tenon and mortise then provide an additional seal to gas leaks between the interior chamber and the flow stream, all the better that this is achieved by contact of plane surfaces. It then becomes possible to reduce the contact width between the spacer and ring rims, which provides the advantage of then lowering the heat transmissions from ring 3 to spacer 2.
Another enhancement now becomes possible: the clips which keep the rims clamped may have their core accommodated in the notches of these rims, which does not effect in any way the seal of the joint as the rims are separated at the location of the notches; but by pushing the cores of the clips towards the notches, their protruding outside the rims is prevented and the bulk size of the whole is thereby reduced; furthermore, the clips are used from now on for limiting the angular slipping movement of the rings of the spacer, by abutting against the side faces of the notches. So the pins of the prior realization and their bores which were the center of significant stress concentrations may therefore be suppressed. The notches are also responsible for the stress concentrations but which are less significant, because of their dimensions and their more regular shape.
The presence of the tenon on the ring is also advantageous, as generally the ring is made in monocrystalline material which is rather difficult to machine; it is seen that it is less difficult to produce a tenon than a mortise. The spacer is generally built in a material which is easier to machine, so that the mortise may be produced easily thereon, for example by forming a tab thereon, which contributes to surrounding the mortise in connection with an adjacent portion of the spacer.
There is nothing up to the opposite side, bearing the hooks, which may not be enhanced according to the invention: the ring hook may cover the spacer hook, unlike the prior design, which here again, also has the advantage of locally protecting the spacer from heatings produced by the stream.